This invention relates to electron-emitting devices. More particularly, this invention relates to the structure and fabrication, including testing, of an electron-emitting device suitable for use in a flat-panel display of the cathode-ray tube (xe2x80x9cCRTxe2x80x9d) type.
A flat-panel CRT display basically consists of an electron-emitting device and a light-emitting device that operate at low internal pressure. The electron-emitting device, commonly referred to as a cathode, contains electron-emissive elements that emit electrons over a wide area. The emitted electrons are directed towards light-emissive elements distributed over a corresponding area in the light-emitting device. Upon being struck by the electrons, the light-emissive elements emit light that produces an image on the viewing surface of the display.
Specifically, the electron-emissive elements are conventionally situated over generally parallel emitter electrodes that are opaquexe2x80x94i.e., impervious to light, typically ultraviolet (xe2x80x9cUVxe2x80x9d) and infrared (xe2x80x9cIRxe2x80x9d) light as well as visible light. In an electron-emitting device that operates according to field-emission principles, control electrodes typically cross over, and are electrically insulated from, the emitter electrodes. A set of electron-emissive elements are electrically coupled to each emitter electrode where it is crossed by one of the control electrodes. The electron-emissive elements are exposed through openings in the control electrodes. When a suitable voltage is applied between a control electrode and an emitter electrode, the control electrode extracts electrons from the associated electron-emissive elements. An anode in the light-emitting device attracts the electrons to the light-emissive elements.
The electron-emitting device in a flat-panel CRT display commonly contains a focusing structure that helps control the trajectories of the electrons so that they largely only strike the intended light-emissive elements. The focusing structure normally extends above the control electrodes. The lateral relationship of the focusing structure to the sets of electron-emissive elements is critical to achieving high display performance. In fabricating the electron-emitting device, the opaque nature of the emitter electrodes can present an impediment to achieving the requisite lateral spacing between the focusing structure and the sets of electron-emissive elements. Accordingly, it would be desirable to configure the emitter electrodes in such as way as to facilitate controlling the lateral positions of components, such as the focusing structure, in the electron-emitting device.
Short circuits sometime occur between the control electrodes, on one hand, and the emitter electrodes, on the other hand. The presence of a short circuit can have a very detrimental effect on the display""s performance. For example, a short circuit at the crossing between a particular control electrode and a particular emitter electrode can prevent part or all of the set of electron-emissive elements associated with those two electrodes from operating properly. It would also be desirable to have a way for configuring the emitter electrodes to facilitate removal of short-circuit defects.
In the present invention, an emitter electrode for an electron-emitting device is formed generally in the shape of a ladder. That is, a line of emitter openings extend through the emitter electrode. During fabrication of the electron-emitting device, the emitter openings can be utilized in a manner that permits features, such as a focusing system, to be self-aligned to other features, such as control electrodes, so as to achieve desired lateral spacings in the device.
For example, when at least part of the focusing system is created from actinic material, portions of the control electrodes typically overlie the emitter openings in the ladder-shaped emitter electrode. The actinic material is selectively exposed to backside actinic radiation that passes through the emitter openings. During the backside exposure, the portions of the control electrodes overlying the emitter openings serve as part of a radiation-blocking mask that results in edges of the focusing system being self-aligned to parts of the edges of the control electrodes. Similar self-alignment is achieved in creating other structures from actinic material using the control electrodes or other such features extending over the emitter openings as part of a mask for blocking backside actinic radiation that passes through the emitter openings.
The ladder shape of the present emitter electrode also enables defects such as short circuits to be removed from the electron-emitting device without significantly impairing device performance. In particular, the present emitter electrode typically contains a pair of rails connected by crosspieces. If a short circuit between the emitter electrode and an overlying control electrode occurs at one of the crosspieces, that crosspiece can be cut out of the emitter electrode. Likewise, if a short circuit occurs at one of the two rails at a location below a control electrode, that portion of the rail can be cut out of the emitter electrode. In either case, removal of the indicated portion of the emitter electrode does not significantly impair the ability of voltage to be impressed through the remainder of the emitter electrode.
Short-circuit removal can be performed through the back side (bottom) of the electron-emitting device utilizing a suitably focused energy beam such as a laser beam. Openings can be provided in the control electrodes to permit all short-circuit removals to be performed through the front side (top) of the electron emitter. The crosspieces of the ladder-shape emitter electrode can be specially shaped to facilitate short-circuit removal. For example, the ends of each crosspiece can neck down in width, thereby making it easier to cut through a crosspiece when necessary.
In short, the invention overcomes fabrication difficulties arising from the fact that the material of the emitter electrode is normally opaque and thus largely non-transmissive of actinic radiation. The openings in the present emitter electrode permit certain edges in the electron-emitting device to be self-aligned to other edges, thereby enabling certain critical spacings in the device to be well controlled. Device performance is improved. By facilitating short-circuit removal, the general ladder shape of the present emitter electrode leads to increased fabrication yield. The invention thus provides a significant advance.